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The following abbreviations are commonly used to describe the length of a DNA/RNA molecule:

• kbp = kilo base pairs = 1,000 bp
• Mbp = mega base pairs = 1,000,000 bp
• Gbp = giga base pairs = 1,000,000,000 bp

In case of single stranded DNA/RNA we talk about Nucleotides, abbreviated nt (or knt, Mnt, Gnt), rather then base pairs, as they are not paired.

The following figure shows the chemical structures of properly base-paired nucleic acids.

The larger nucleic acids, adenine and guanine, are members of a class of doubly-ringed chemical structures called purines; the smaller nucleic acids, cytosine and thymine (and uracil), are members of a class of singly-ringed chemical structures called pyrimidines. Purines are only complementary with pyrimidines: pyrimidine-pyrimidine pairings are energetically unfavourable because the molecules are too far apart for hydrogen bonding to be established; purine-purine pairings are energetically unfavourable because the molecules are too close, leading to electrostatic repulsion. The only other possible pairings are GT and AC; these pairings are mismatches because the pattern of hydrogen donors and acceptors do not correspond.

As hydrogen bonds are not very strong, the two nucleotides will separate on temparatures higher then 94 C.

Chemical analogs of nucleotides can take the place of proper nucleotides and establish non-canonical base-pairing, leading to errors in DNA replicationDNA polymerase (green) binds to one strand of the DNA. It moves along the strand, using it as a template for assembling a leading strand (red) of nucleotides and reforming a double helix. Then a second DNA polymerase molecule (also green) is used to bind and DNA transcriptionIn genetics, transcription is the first process in gene expression. In transcription, DNA is copied to RNA by an enzyme called RNA polymerase (RNAP). Transcription to yield an mRNA is the first step of protein biosynthesis. Bacterial transcription A (simp. Some analogs are carcinogenIn pathology, a carcinogen is any substance or agent that promotes cancer. Carcinogens are also often, but not necessarily, mutagens or teratogens. Carcinogens cause cancer by altering DNA in cells, interfering with normal biological processes. Usually ces; others are chemotherapyChemotherapy (pronounced keem-o-therapy is the use of certain drugs to treat disease, as distinct from other forms of treatment, such as surgery. Chemotherapy dates at least as far back as the use, by the Indians of Peru, of cinchona bark in the treatment drugs.

1 Intramolecular base pairs

RNA can form intramolecular base pairs. These form a loop and a chain off the main RNA.

2 See also

• Nitrogenous baseNitrogenous bases are the parts of RNA and DNA that are involved in pairing up (see also base pairs). These include cytosine, guanine, adenine, thymine ( DNA) and uracil ( RNA). These are abbreviated as C, G, A, T, and U, respectively. The four bases incl
• Wobble base pairinosine A wobble base pair is a G-U and I-U / I-A / I-C pair fundamental in RNA secondary structure. It has comparable thermodynamic stability of the Watson-Crick base pair. Wobble base pairs are critical for the proper translation of the genetic code.